Cardiac effects of tyramine.

• Tyramino (p-hydroxyphenylethylamine), the product of decarboxylation of tyrosine, has been known for a number of years to have pharmacological activity as a pressor substance." In a preparation of the atrium of the cat's heart in Locke-Ringer solution, Ajidrus, in 1 924, showed that tyramine increased the rate aud amplitude of atrial contractions. In 1926, Tainter reported the circulatory effects of tyramine. Its pressor action was considered to be sympathetic in cats and muscular in dogs. The isolated cat heart showed increased rate and force of contraction. In 1930, Burn demonstrated in the dog heartlung preparation, by means of a cardiometer attached to a piston recorder, a diminution of the cardiac volume with 0.09 mg. tyraniine. He found the action of tyramine on the heart-lung preparation to resemble that of epinephrine with the potency of tyramine being about 40 to 50 times weaker. Muller, in 1937, by means of a continuous volume recorder, demonstrated in the dog heart-lung preparation an average decrease of cardiac volume of 16 cc. with 0.1 mg. tyramine. The maximum effect was reached after approximately three minutes. The duration of the effect was about 15 minutes. The heart rate was usually accelerated. The coronary circulation was augmented and the pulmonary arterial pressure reduced. Bejrablaya, Burn, and Walker, in 1958,° showed that tyramine (0.4 to 2 mg.) in the dog heart-lung preparation increased the heart rate 25 to 82 beats per minute. This effect on the rate was slow in appearing, reaching a peak after approximately seven to eight minutes but lasting 30